Polymerization employing amidines having azo groups



Patented June 3, 1952 POLYMERIZATION EMPLOYING AMIDINES HAVING AZO GROUPS Robert W. Upson, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application June 23, 1950, Serial No. 170,028

This invention relates to the polymerization of ethylenically unsaturated compounds and more particularly to the polymerization in water systems by means of water soluble azo compounds which contain amidine, i. e., guanyl, groups in the form of their acid salts.

In U. S. 2,471,959 it has been shown that certain organic azo compounds which have an acyclic azo group bonded to aliphatic carbons of a particular character are useful as polymerization initiators, or catalysts, for polymerizable ethylenic compounds. These catalysts have several advantages over the more conventional type which have directly linked oxygen atoms, such as benzoyl and other peroxides. The latter type polymerization initiators provided a source of oxygen which may change the properties of the polymer obtained by discoloration, oxidation of any added modifiers and insolubilization.

The azo compounds disclosed in U. S. 2,471,959 represent a considerable advance in polymerization; however, the compounds disclosed are generally water insoluble particularly in slightly acid media and accordingly not convenient to employ in the direct preparation of polymer dispersions by the polymerization of polymerizable ethylenically unsaturated compounds in water systems at relatively low temperatures.

-It is disclosed in U. S. application Serial No. 757,682, filed June 27, 1947, now U. S. Patent 2,520,338 that carboxylic groups be introduced in one of the hydrocarbon chains of the azonitriles. The akali metal salts of such carboxylic azonitriles have some solubility in aqueous systems which are neutral to basic. However, it has been found that these compounds are not soluble in aqueous acidic solutions. Acidic solutions are preferable for many polymerization reactions, particularly those involving olefinic hydrocarbons and certain acrylic compounds, to obtain superior properties in the resulting polymers.

In general, the use of peroxy and other prior art polymerization catalysts in the polymerization of ethylene in aqueous media has resulted in formation of a coagulated polymer. For many uses, a dispersion of ethylene polymer in water would be an advance in the art provided the dispersion was of sufficient concentration, e. g., above 15% of polymeric ethylene, and of high quality, e. g., high molecular weight but relatively free from crosslinking. Such a dispersion pos- '7 Claims. (Cl. 26094.9)

generally required too high a temperature to produce high quality polymer in dispersed form.

This invention has as an object a new process of polymerization. A further object is the provision of new polymerization systems. Otherobijects will appear hereinafter.

These objects are accomplished by theinven tion of the process wherein a monomer subject to addition polymerization and having a nonaromatic ethylenic group, preferably terminal, is polymerized by bringing the monomer in com tact with an organic azo compound wherein the azo N=N group is acyclic and bonded'from both of the nitrogens to discrete carbons which are aliphatic and at least one and generally both of which discrete carbons are tertiary and have as one of the groups attached to the tertiary carbon a guanyl radical in the form of an inorganic acid salt. These azo amidine catalysts are particularly useful in the preparation of polymer dispersions in aqueous media. The preferred compounds are thus acid salts of dialkyldiguanylazoalkanes in which the alkyl radicals are lower alkyls, particularly of from one to four carbons, for use in the polymerization.

In general these compounds may be prepared by the treatment of an azonitrile, e. g., alpha,- alpha'-azodiisobutyronitrile, in an anhydrous system with an alcohol, hydrogen halide and a hydrogen-bearing amine of the formula HNRz where R. is hydrogen or an organic radical, generally hydrocarbon, of one to six carbons. These compounds are generally employed in amounts of from 0.1 to 5% based on the weight of ethylenically unsaturated compound in an aqueous medium at temperatures of from 40-90 C. and generally in the presence of a surface-active agent.

The following examples in which parts are by weight are illustrative of the invention.

Example I A solution of ten parts of purified commercial sodium dodecylsulfate and four parts of 'disodium hydrogen phosphate in 200 parts of distilled oxygen-free water was prepared under nitrogen. This solution was cooled in ice and one part of the hydrochloride of 2,2-diguanyl-2,2-azopropane was added. The resulting mixture was charged in a stainless steel-lined rocker bomb capable of holding 1000 parts of water. The bomb was then flushed with nitrogen and evacuated. Ethylene was added until the total pressure was 500 atmospheres. The contents oft-he bomb were heated to C. and the. pressure then raised to 900 atmospheres by the addition of more ethylene. The reaction mixture was agitated by rocking the bomb for two hours While the temperature was maintained at 70 C. At the end of this period the temperature was lowered and the ethylene bled ofi. The reaction mixture (which corresponded in volume-t 210'parts' of water) at this point was a transparent liquid with a bluish cast. A portion (weighing about 110 parts) of this material was acidified by the addition of dilute nitric acid and then heated toboiling until the ethylene polymer was completely coagulated; The polymer was removed by filtration and washed with acetone and-water, then air dried to give 27.5 parts of white powder which-corre-- sponds to a solids content of 25% in the original dispersion. The ethylene polymer hadan inherent viscosity of 0.58 as determined on a 0.1% solution in Xylene at 85 C.

Example II 'Ihe procedure 'of Example I was repeated except: that=the reaction time: was four 'hours: at 65? C..and;no disodium hydrogen phosphate was present; I'he volume of dispersion isolated cor responded (involume) to 2-28 partsofiwater; the solids content was 27.5%; and-the-ethylene polymer had'an inherentviscosity of 0.50.

Example III The-general procedure of'Example' III was repeated except that the-monomer system consisted of 19 parts of acrylonitrile; and one partofdi- 'methylaminoethyl methaorylate and the polymerization timewas 18* hours at a pH of 9.35. There was obtained-1352 parts (65% conversion) of polymerwhich had aninherent viscosity of 2.7.

Example V A mixture consisting of '186 parts of water, 12.3

parts of 'acrylonitrile, 0. 7part of-dimethylaminoethyl-'m'ethacrylate; and-0.07 part of the hydrochloride of 2,2 diguanyl-2,2'-azopropane was adjusted'to-a pHof 3.93 with sulfuric acid; charged inagl'ass vessel, fiushed with :nitrogen andisealed.

After.- 70minutes at65" C. there was obtained a 66% conversion to a polymer Which-had anainherent:viscosityof 3.84;

Example VI A glass container was charged with 20 parts of water, 16 parts of acrylonitrile and 0.2 part of the hydrochloride of 2,2'-diguanyl-2,2'-azobutane'. As soon as the temperature was raised to 60 C. rapid polymerization took place.

Example VII The general procedure-of Example VI was repeated except that the azo compoundwas 2,2"- bis(N,N- diethylguanyl) 2,2 azopropane. A white polymer was obtained.

Example VIII.

When. the general procedure of Example'VI was' repeated except that the azo compound employed was 2,2-bis(N-hydroxyethylguanyl)-2,2'- azopropa-ne', polymerization also occurred.

Example IX A glass vessel was charged with 11.6 parts of allyl alcohol, 10.6 parts of acrylonitrile, parts of water and 0.1 part of 2,2-diguanyl-2,2-azopropane. After heatingfor 16 hours. at C., a. total of:3.8 parts of polymer was obtained which contained 73.7% acrylonitrile.

Example X A-mixture of 100 parts of 2-chlorobutadiene, 4 partsaoffNancy wood rosin and 0.4 part of dodecyl mercaptan was added to a solution containing 15.7 partsof distilled'copper-free water, 1.15 parts of sodium hydroxide, 06 part of Daxad 11 (a dispersant and 1.5 parts of 2,2'-diguanyl-2,2'- azopropane. The resultant emulsion was stirred under nitrogen for 25 minutes at 60 C. The polymerization was stopped by the addition of a small amount of an emulsion containing p-tertiarybutylcateohol and phenothiazine. The polymer was isolated by coagulation with methanol and brine and the plastic tacky rubber washed" and driedon-a mill at 50-60 C. There was-obtained 38 parts-of polymer.

Example: XI

A glass vessel was charged with 34 parts of methyl-hydrogen maleate, 27 parts of'acrylonitrile, 740 parts ofwater and 0.3 part of '2,2'-diguanyl-2,2'-azopropane. After fivehours at' C. a 20% conversion topolymer was obtained. Thepolymer had an inherent viscosity (0.2% solutionin' dimethylformamide) of 1162 andhad a softening temperatureof 190 C. Theproduct contained 24.64% nitrogen corresponding to a copolymer" containing 6% methyl hydrogen maleate.

A- preferred systemof'the present invention wherein ethylene ispolymerized in aqueous media employing the azoamidines of this invention as catalysts-is illustrated inEXample XII below.

Example XII.

A solution of six parts"commercialiTriton X; 300 parts of copper-free, deoxygenated water and 30 parts of tertiary butyl alcoholwas prepared and charged under-nitrogen at room temperature to a rockerbomb having a" stainless-steel liner and a capacity of 1500 parts. by weight of water; 0.5 part of the hydrochlorideof 2,2-diguanyl-2;2-azopropane was added to the bomb which was then flushed with nitrogen, closed, and evacuated. Ethylene was added (565 atmospheres of pressure) to the bomb which was then heated to an internal temperatureof 65"'C. Additional ethylene was charged to the bomb 'till a pressureof 970-atmospheres was-obtained.- The reaction mixture was then agitated by rocking for a period of six hours while the temperature was maintainedat 65" C. and the pressure was held between 900' and 1000 atmospheres by'repressuring with ethylene. A' total pressure drop of atmospheres I was recorded during-the reaction period. At the end of the reaction the bomb was cooled and the excess-ethylene was bledoff. A milky white; fluid liquid was recovered. Assayofi the dispersion indicated-the presence: of' 11.3%: solids and electron: photomicrographs indicated that the dispersed particles were: spheroidal and approximately 0.1 micron inidiameter; A portion. of the liquid was treated with a large volume of acetone and the coagulate'd polymer. was filtered, washed with acetone and water, and dried. This material had an inherent: viscosity of 1.58 as determined on'a '5 solution containing 0.1 g. polymer/100 cc. of xylene at 85 C. A film pressed at about 140 C. was very flexible and orientable.

The present invention is generic to the polymerization of ethylenic monomers subject to addition polymerization, employing as the initiator orcatalyst, a soluble acid salt of an azo-compound which contains a g'uanyl radical attached to a tertiary carbon which carbon is further attached to an acyclic azo group. The following general formula shows the preferred compounds:

wherein R and R'=alkyl radicals of one to four carbons, e. g., methyl, ethyl, n-butyl, and R"=I-l, or a monovalent organic radical of one to six carbons, e. g., methyl, butyl, hexyl, phenyl, while HX represents an inorganic acid and suitably a hydrogen halide. In a further preferred embodiment, these compounds are saturated, i. e., free from carbon to carbon unsaturation, and are hyv drocarbon except for the azo and guanyl nitrogens and the acid. The invention is thus applicable inter alia to the hydrochlorides and hydrobromides of 2,2'-bis (N-phenylguanyl) -2,2-azopropane, '2,2-bis(N,Ndimethylguanyl) -2,2'-azomerizable monomer isgenerally within the range of 3-to 20 per part of monomer thatis converted to polymer.

The particular surface-active agent or dispersant employed, if any, is subject to wide variation. In fact any of the three different types, i. e., nonionic, anionic, and cationic, may be employed. The precise amount employed in systems in which the polymerizable monomer is insoluble depends upon the activity of the dispersant. Amounts of 1 to 10% are generally employed.

Liquid conditions are desired for the polymerization of this invention and polymerizations in which the monomer is a gas require pressure.

1 Thus ethylene polymerizations generally are effected at pressures of from 100 to 7500 atmospheres. Y 1

In that modification of the invention represented by Example XII above the polymerization system includes not only the monomer, catalyst, and initiator, but also a water-miscible organic solvent and a dispersing agent. The'water-miscible organic solvent is present in amountsof 5 to 30% of the weight of water employed. Particularly suitable are the lower aliphatic (1 to 4 decomposition with, for example, lead nitrate,

silver fluoride, or by freeing the amidine base i? with'the useof alkali followed by acidification of the base with the appropriate acid, e. g., hydriodic, sulfuric, etc. 7 The azo catalysts of this invention can be prepared by a process comprising (a) reaction in an anhydrous alkanol of hydrogen chloride or 'hydrogen bromide with an organic azo compound wherein the azo, N=N-, group is acyclic and bonded from both its nitro'gens to discrete carbons one at least ofwhich is tertiary and has attached to it anitrile group, (1)) separation of the salt thus obtained, and (0) treatment with a hydrogen-bearing amine including ammonia, aniline, diphenylamine, diethylamine, in alkanol medium. The above reactions are carried out under anhydrous conditions and at temperatures of generally in the range of 10 to C. This preparation is exemplified in my copending application Serial No. 170,027, filed of even date herewith, wherein the azo amidines are claimed as new compounds. The preferred azonitriles are saturated and are hydrocarbon except for the nitrile and azo nitrogens.

Azonitriles from which the guanyl salts are prepared can be obtained by the procedure of Thiele and Heuser, Ann., 1-43 (1896), Dox, J. Am. Chem. Soc. 47, 1471-1477 (1925) and Alderson and Robertson U. S. 2,469,358.

The amount of the azo catalyst employed can vary within wide limits although generally 0.05 to meric material for use, the ratio of water to polycarbon) alcohols and particularly the alkanols such as methanol and tertiary butyl alcohol. Although anionic (e. g., sodium lauryl sulfate) or cationic dispersing agents may be employed, nonionic dispersants are preferred, such as polyethylene oxide derivatives of phenols (e. g.,Triton X). The amount of dispersant present may vary considerably but is generally at least 1 and may be 3% or more based on the amount of water employed. V The products obtained by the process of Example XII have superior properties; i; e., the emulsions can be used directly or the polymer can be isolated and fabricated into-films or molded objects. These polymers are orientable and exhibit oustanding flexibility. Viscosity of the polymer solutions in hot xylene is high.

The process of this invention is of generic application to the addition polymerization of polymerizable compounds having the non-aromatic ethylenic,

group. It is particularly applicable to monomeric unsaturated polymerizable compounds in which the unsaturation is due to a terminal ethylenic'group which is attached to a negative radical. It is thus applicable to polymerizable vinylidene compounds, including vinyl compounds and particularly preferred are those which contain the group.

Compounds having a terminal methylene, CH2=, group which are subject to polymerization and copolymerization with the initiators of this invention include olefins, e. g., ethylene, isobutylene; acrylyl and alkacrylyl compounds, e. g., acrylonitrile, methyl acrylate, ethyl methacrylate, methacrylic acid, methacrylamide; vinyl and vinylidene halides, e. g., vinyl chloride, vinylidene chloride; vinyl carboxylates, e. g., vinyl acetate, vinyl trimethylacetate; vinyl imides, e. g., N- vinylphthalimide; N-vinyllactams, e. g., N-vinylcaprolactam; vinyl aryls such as styrene and mer.

.7 other vinyl derivatives such as the vinylpyridines, methyl 'Vin'yl ketone and vinyl ethyl ether.

Fluoroethylenes including ,vinyl fluoride and particularly polyfluoroethylenes, including tetrafl-uoroethylene, chlorotrifluoroethylene and 1,1-

dichloro-2,2difiuoroethylene maybe polymerized containtwo or more double bonds which are isolated withrespect to each other, such as ethylene glycol dimethacrylate, 'methacrylic anhydride, diallyl m'aleate and divinylbenzene.

In addition to copolymers obtainable from the classes of monomers mentioned above, the co polymerization of fumaric'or maleic esters, carbon monoxide, sulfur dioxide, and/or acetylene with types of monomers mentioned, can be effected by the process of this invention. Furthermore,;-the term polymerization includes within itsscope (in addition to the polymerization of a monomer'alone or of two or more monomers, i.-e., copolymerization) the polymerization of unsaturated monomers in the presence of chain transfer agents, e. g., carbon tetrachloride.

This latter process has been called telomerization. See U. $2,440,800.

This invention is applicable to the polymerizationof any. unsaturated compound subject to addition polymerization by prior techniques.

Optimum conditions may vary from monomer to monomer, and since liquid phase polymerization is desired, gases such as ethylene and propylene require pressure.

The process of this invention is particularly .useful "for the preparation of dispersions of fusible'polymers and particularly of ethylene poly- The dispersions canbe used for casting of film and preparationof coatings or applying the polymer dispersions'to cloth, paper, etc. In view of the absence of peroxy catalyst residues, the films thus obtained are of superior quality.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious -modifications will occur to those skilled in the art.

What is claimed is: -1. In'the addition polymerization of ethylenically unsaturated gmonomers subject :toaddition polymerization, the improvement wherein the monomer is brought in aqueous dispersion into contact with, as an initiator of the polymerization, an inorganic acid salt :of an organic azo compound wherein the acyclic azo, -N=N-, group is bonded to two discrete aliphaticcarbons one, at least, of which is tertiary and :bonded-to a guanyl radical. V

2. In the addition polymerization of ethylenically unsaturated monomers subject to addition polymerization, the improvement wherein the monomer is brought in aqueous dispersion into contact with, as an initiator of the polymerization, an inorganic acid salt of an aliphatic azo compound of the formula wherein R and R are alkyl radicals of one to four carbons, R" is selected from the class consisting of hydrogen and organic radicals of one to si-x'carbons and HX is an inorganic acid.

3. In the addition polymerization of ethylenically unsaturated "monomers subject to addition polymerization, the improvement wherein the monomer is brought in aqueous dispersion into contact with, man initiator of the polymerization, an inorganic acid salt-of an aliphatic azo compound wherein the acyclic azo; --N:N, group is bonded to two discrete tertiary aliphatic carbons each bonded to a guanyl radical.

4. Process of claim 3 wherein the guanyl radical of the azo compound is unsubstituted and the aliphatic azo compound in free base form is saturated hydrocarbon except for the azo and guanyl nitrogens.

5. Process of claim 3 wherein the azo compound in free base form is 2-,2-diguanyl-2,2-

azopropane.

6. Processof claim 2 wherein the monomer is.

ethylene.

'7. Process of claim 5 wherein the monomer is ethylene.

ROBERT W. UPSON.

Name Date Hunt May 31, 1949 Number 2,471,959 

2. IN THE ADDITION POLYMERIZATION OF ETHYLENICALLY UINSATURATED MONOMERS SUBJECT TO ADDITION POLYMERIZATION, THE IMPROVEMENT WHEREIN THE MONOMER IS BROUGHT IN AQUEOUS DISPERSION INTO CONTACT WITH, AS AN INITIATOR OF THE POLYMERIZATION, AN INORGANIC ACID SALT OF AN ALIPHATIC AZO COMPOUND OF THE FORMULA 